1. Field of the Invention
The present invention relates to a substrate formed on a base material and having a barrier film for preventing copper diffusion, which is used as a barrier and catalytic layer of ULSI fine copper wiring.
2. Description of the Related Art
It is well known that a copper film for ULSI fine copper wiring (damascene copper wiring) can be formed by copper electroplating using a seed layer formed by electroless plating.
Conventionally, it has been difficult to obtain sufficient adhesiveness with a deposited plating film when electroless copper plating is performed on a mirror surface such as a semiconductor wafer. The plating also has poor reactivity, making it difficult to plate the entire substrate surface uniformly. Conventionally, it has been difficult to form a uniform plating film and adequate adhesiveness thereof has not been obtained when forming a copper seed layer by electroless plating on a barrier metal layer of tantalum nitride or the like.
The inventors in this case discovered previously that by adding a water-soluble nitrogen-containing polymer with a small weight-average molecular weight (Mw) as an additive to an electroless copper plating liquid, and affixing a catalytic metal to the substrate to be plated before immersion in the liquid, or else forming a film of a catalytic metal on the outermost surface and then immersing it in the plating liquid to adsorb the polymer via nitrogen atoms on the catalytic metal, it was possible to control the plating deposition rate and crystals become extremely fine, allowing the formation of a uniform thin film with a film thickness of 15 nm or less on a wafer or other mirror surface (Japanese Patent Publication No. 2008-223100). In the examples of this reference, the inventors also showed that by first forming a film of a catalytic metal on the outermost surface and then immersing it in the plating liquid to adsorb the polymer via nitrogen atoms on the catalytic metal, it was possible to control the plating deposition rate and the crystals become extremely fine allowing the formation of a uniform thin film with a film thickness of 6 nm or less on a wafer or other mirror surface.
In such a method, or in other words in damascene copper wiring formation, a barrier layer for preventing copper diffusion must be formed in advance separately from the catalytic metal layer when a copper seed layer is provided by electroless plating after formation of the catalytic metal film, and two layers, a barrier layer and a catalytic metal layer, are formed before forming the copper seed layer. Therefore, it was difficult to apply this method to actual processing of ultrafine wiring, which cannot have thick films.
To eliminate the complication of forming two layers prior to forming the copper seed layer, the inventors in this case discovered that by forming a single layer consisting of a specific alloy thin film having both a barrier function and a catalytic function, and combining displacement plating with reductive plating for electroless plating, it was possible to form a thin copper seed layer thereon with a uniform thickness, and submitted patent applications (PCT/JP2008/063023, PCT/JP2008/063024). However, such an alloy thin film having both a barrier function and a catalytic function has an insufficient barrier properties when the film is heated to a high temperature of about 500° C., and there has been a need for greater reliability especially during long-term use in a semiconductor device.